This project will compare the therapeutic efficacy of 3 vitamin D agents in the treatment of uremic renal osteodystrophy in children: Dihydrotachysterol (DHT); 25-hydroxyvitamin D3 (25(OH)D3): 1,25-dihydroxyvitamin D3 (1,25(OH)2D3. These drugs will be assigned randomly to 3 matched groups of children who will be followed for a period of three years. Baseline characterization of renal osteodystrophy will include clinical, routine biochemical, radiographic, hormonal (e.g., serum levels of PTH) and histomorphometric measurements, the latter made on percutaneous transilial bone biopsies obtained at yearly intervals. Plasma levels of 25(OH)D3 and 1,25(OH)D3 will be followed pre- and post-treatment both to monitor the effects of treatment on vitamin D metabolism and to assess drug toxicity. To date, approximately 40% of the anticipated 30 patients for the trial have been fully evaluated in the screening phase of the protocol; 2 matched groups of 3 patients each are about to commence therapy. Our laboratory has established normal pediatric values for plasma 25(OH)D3 and 1,25(OH)2D3, compared these to levels obtained from a group of pediatric patients with various defined levels of chronic renal failure, and examined the effect of 25(OH)D3 therapy on plasma 25)OH)D3 and 1,25(OH)2D3 levels in a previously studied group of children with renal osteodystrophy.